Cladding of lower alloyed steels with stainless steel surface layers is a widely used method of cost saving in the construction of industrial equipment that must be resistant to corrosion. The stainless steel layer may be bonded to a base material -- such as carbon steel -- by rolling, by explosion bonding, or even by casting bimetallic ingots and rolling them. All of these methods are limited to simple shapes, such as plates, and cannot be readily used where the clad material must be fabricated by such methods as casting or welding.
An economical and versatile method for cladding is the method known as overlay welding. In this method, a layer of stainless steel is applied to a base material by melting the stainless steel onto the surface of the base material by welding techniques. Newer overlay welding techniques have developed to the point where electrodes in the shape of strips or ribbons are used instead of electrodes in the shape of bars or wire in that covering the surface completely can be accomplished much more readily employing strip electrodes. The metal deposition rate can be higher when using strip electrodes because the larger cross-section area of strip permits carrying higher currents.
Use of overlay welding is increasing, particularly in industries where corrosion-resistant storage vessels are employed. One difficulty with overlay welding is that the austenitic stainless steels are difficult to apply to a base material by overlay welding techniques because the austenitic stainless steel is subject to hot cracking when applied by overlay welding. Experience has shown that stainless steel containing some delta ferrite is much less susceptible to cracking compared to austenitic stainless steel, or not susceptible to cracking at all when used for overlay welding. Unfortunately, austenitic stainless steel having a separate delta ferrite phase within it is so difficult to hot work that manufacturing of electrodes of this material is very expensive. The difficulty in hot working stainless steel increases with increasing amounts of delta ferrite up to where ferrite becomes the continuous phase.